Ambiguity estimation of GNSS signals for three or more carriers is disclosed in Vollath U.S. Pat. Appl. US 2005/0101248 A1, published May 12, 2005. Relative position measuring techniques using both GPS and GLONASS carrier phase measurements are described in Kozlov et al. U.S. Pat. No. 5,914,685, dated Jun. 22, 1999, and in Kozlov et al. U.S. Pat. No. 6,229,479 B1, dated May 8, 2001. A receiver using signals of GLONASS and GPS systems is described in Rog et al. U.S. Pat. No. 6,441,780 B1, dated Aug. 27, 2002. Navigation data prediction for GPS and GLONASS weak signal tracking is described in Vorobiev et al. U.S. Pat. No. 6,731,701 B2, dated May 4, 2004. Improved methods and apparatus for ambiguity resolution using multiple GNSS and/or GNSS that employ FDMA are desired, as will become apparent from the description below.